1. Field of the Invention
The present invention relates generally to apparatus for controlling cursor movement on a cathode ray tube (CRT) and more particularly to such apparatus which is integrated with a keyswitch on a keyboard.
2. Description of the Related Art
Prior art pointing devices for controlling a cursor on a CRT are known. What others have failed to appreciate is the ergonomic implications of mechanical and electrical null regions which must be traversed at the outset of a pointing operation. Using prior art devices, even those that are force-sensitive, a user gets no response to lateral displacement initially, until an electrode makes initial contact, for example, with an elastomeric resistive layer. The initial contact causes a step response, as resistance drops from infinity to a measurable value--a jump the user may not have anticipated or desired. Then, as force is increased, resistance falls rapidly, over some range, and finally falls more slowly with the application of additional force. All of this is disconcerting to a user for most applications. What is needed is to provide for pointing which is smoothly and consistently responsive to user input from the outset of the pointing operation.
Another disadvantage associated with prior art devices is that they are not sensitive to z-axis force. Forces applied laterally, i.e., in the x-y axis plane move the CRT cursor correspondingly. It would be desirable for a vertical force, e.g., down the shaft of a joystick-type controller, to produce a proportional signal. Such a signal could be used for example to control line width while drawing as a function of z-axis force on the pointing device.
Pointing devices which are integrated into keyswitches on keyboards are also known in the prior art. In addition to suffering from the above-described disadvantages associated with prior art pointing devices, such integrated devices take up substantially more space than a conventional key switch.
One prior art cursor control is shown in U.S. Pat. No. 4,313,113 (Thornburg). It employs four orthogonal variable resistance pressure transducers, each transducer comprising a coordinate electrode spaced from a cooperating electrode, at least one of the electrodes being an elastomeric sheet material formed of a carbon loaded polyolefin. The path resistance through the transducer goes down as applied pressure goes up. Thornburg recognizes the advantage of using force to control cursor speed. It makes no suggestion to integrate the device into a regular keyswitch. The electrodes are spaced from the elastomeric layer, at rest, so that there is a mechanical and electrical null region before the system responds to a force input, followed by a step response when the electrode layers make initial contact.
U.S. Pat. No. 4,439,648 (Reiner et al.) is directed to a basic stand-alone joystick. The handle rests on a rigid pivot so that vertical force is ignored. The handle is coupled to an actuator portion spaced from all four switches, so there is a neutral or null region of displacement before any switch is closed. The switches are conventional, yielding only a binary signal, without regard to force.
U.S. Pat. No. 4,408,103 (Smith, III) discloses a miniaturized joystick adapted for mounting in a wristwatch. The joystick handle rests in a hollowed-out bearing surface so that none of the switches is actuated by a downward force on the handle. The switch actuating means is maintained spaced from all the switches by a resilient rubber sheet layer, so there is a neutral or null region of displacement before any of the switches is closed. The switches are miniaturized by forming them as interleaved electrodes on a PCB. When the handle is pivoted, an actuator pushes a conductive region of the resilient layer into contact with a corresponding switch. The switches each yield a binary output, so lateral force beyond an initial detent is ignored.
U.S. Pat. No. 4,246,452 (Chandler) shows another joystick type device, here having 16 possible output signals. The mechanism again employs a handle having a depending member that rests in a hollowed out bearing surface. Once again, the switches each provide a binary signal, independent of lateral force beyond a threshold force; vertical force is ignored; and, the actuator is spaced from the switches to provide a null region.
U.S. Pat. No. 4,680,577 (Straayer et al.) suggests a multipurpose cursor control keyswitch that serves both as a regular typing key, preferably in the "home row" (asdf-jkl;) of a keyboard, as well as a force-sensitive pointing input device. The use of strain gauges as shown therein for force sensing, however, is not commercially practical. Additionally, the recent rise in popularity of portable, lap-top and now "notebook" computers makes low profile methods essential.